Performance monitoring circuits are employed to model actual performance of integrated circuits. For example, a ring oscillator circuit can be fabricated on a core of an integrated circuit, such that the ring oscillator is subjected to the same processing, operating and environmental conditions of the integrated circuit. The ring oscillator output frequency can be designed to be a function of the performance of a critical path of the integrated circuit. Therefore, the output frequency of the ring oscillator will change with changes in performance of the integrated circuit. Additionally, the ring oscillator output frequency can model performance degradation of the integrated circuit, since the integrated circuit and the ring oscillator are formed from transistors, which through use degrade in performance over time.
Recently, there has been a growing demand for semiconductor chips with larger density, higher performance and increased chip functionality to meet the continued demand for portable electronic devices. This demand has been partially met with the recent advance in deep sub-micron Complimentary metal oxide semiconductor (CMOS) technology. However, there is also a continuous demand for devices that provide the increased performance but at a reduced power. Therefore, with the employment of submicron CMOS processes to provide the higher performance, it is also desirable to minimize leakage of these transistor devices to minimize power consumption. Therefore, it is important to tailor device operation so a minimum desired performance is maintained, while keeping leakage to a minimum. One method for achieving this is to model the performance of the integrated circuit to the performance of a ring oscillator, and adjusting the supply voltage of the integrated circuit to a minimum operating level to maintain the desired performance of the integrated circuit based on an output frequency of the ring oscillator.